Add `sync patterns` into docs where reusable block(s) are mentioned

[oglekler]

Because reusable blocks are renamed into sync patterns, it looks like we need to have both names alongside in the code docs because we have reusable and block in many places in code and file naming, and it is unnecessary to rename them all, but need to make clear that they are the same thing now.

This adds comments in the docs that patterns and reusable blocks are the same, that patterns is new since 6.3.0.

Trac ticket: https://core.trac.wordpress.org/ticket/59388